Difference between _string.formatter_parser in cpython and rustpython

[kaanyalova]

The outputs of this script are different between rustpython and cpython

import _string

format_string = "{title[:220]}"


for literal_text, field_name, format_spec, conv in _string.formatter_parser(
    format_string
):
    print(
        f"literal_text: '{literal_text}' field_name: '{field_name}, format_spec: '{format_spec}, conv: {conv}'"
    )

cpython prints correctly:

literal_text: '' field_name: 'title[:220], format_spec: ', conv: None'

while rustpython prints:

literal_text: '' field_name: 'title[, format_spec: '220], conv: None'

this seems to cause issues when using gallery_dl as this is used for formatting file names in some extractors

[youknowone]

Thank you for the report.

FormatString::parse_spec which is in our https://github.com/RustPython/Parser repository seems to have a bug.